Bright copper plating bath



Unitedtsratesfi Patent Claims priority, application Netherlands July5j1952 9 Claims. (ClIZM -SZ) The electrolytic deposition of copper is an operation. whichds appliedv very frequently.- in the. metal industry and is carried out either to embellish the surface of the treatedwbjects or to increase the corrosion resistance thereof," while the electro-de'posited" copper als'o serves as a base for a further treatment such-as the electrolytic depositionof nickel. ln'pra'ctice hig'hdemands are made on the appearance of the treated objects'so' that theseup" till now had to be ground and polished in an earlier-or later stageofthe'treatment which entails a number of operations, of whiehithe cost connect'ed therewith form a greatpart of the total cost of the surface:treatment,.theelectrolytic deposition of copper formsa-part of I Mdstelectfolyti'ci baths have the property that they do not fill up unevennesses in -the' metalsurface such as scratches and-the like but rather accentuate them, .and especially the baths for the electro-deposition of bright metal layers, from which a very fine crystalline metal deposit is precipitated, have the property that they, besides covering the uneven metal surface with a bright metal layer, also cover the unevennesses only with a thin layer, due to which the latter, although lustrous, remain visible in an undiminished degree.

It has now been found that the acid copper bath in so far makes a favorable exception on the baths, that it has some filling action, in other words, partially fills up gaps, pits and other unevennesses in the surface so that one aimed at improving the filling action of the copper bath, while maintaining other favorable properties such as the capacity to deposit a soft coating on the metal, etc.

It has been proposed to meet the above-described need by adding an organic substance to the copper bath. It is known e. g. from the U. S. P. 1,903,860 to add thiourea or a water-soluble derivative of thiourea, such as methylthiourea, to metal baths. It has been found, however, that the copper coating which is precipitated from the copper baths thus prepared, is very hard, so that it easily springs off on bending and moreover has a very small lustrous range which is considered as a very serious drawback of these baths. Moreover, the action of a copper bath containing exclusively thiourea as an organic compound decreases very soon. 7

It has now been found that a soft copper layer is obtained if the combination of thiourea or a water-soluble derivative of thiourea and a water-soluble heterocyclic nitrogen compound is added to an acid copper bath. The bath thus prepared displays moreover an excellent filling capacity and has a wide lustrous range.

According to the invention objects, particularly metal objects, are electrolytically provided with a copper deposit with the aid of an acid bath by using a bath con taining the combination of a water-soluble derivative of thiourea and a water-soluble heterocyclic nitrogen compound.

The invention extends to the preparation of an acid copper bath containing the combination of thiourea or a added tothe-bath in combination with the heterocyclic nitrogen compounds allyl thiourea is preferred as well" I 2,742,413 Patented Apr. 17,1956

water-soluble "derivative of thiourea and a water-soluble heterocyclic"nitrogencompound, as well'as to objects electrolyticallyprovided with a copper layer with the aidbf are bath:

Of themvatensoluble hetero'cyclic nitrogen compounds which are*used'in combinatiomwith thiourea or a watersoluble iderivative' of thiourea in theacid copper bath,

compoundsioflthe :xanthine group, particularly-the methyl 1 nonro1ogues'; --sueh as caffeine (l,3;7-trimethylxanthine),-

theophyllirie (1,3-dimethylxanthine) and" theobromine (3,f7-'dimethy1xanthine) are preferred," as well as hexa-=- methylene itetr'ami'ne; morpholine' and pyridine; as well as the ring systems, containing the pyridine nucleus,-=such as quinoline.

Of the'water-soluble thiourea derivatives -which are as acetylthiourea, ,while the thiourea itself, possible;

still exceeds in activity, these two. above-mentioned thiourea derivatives.

The invention is elucidated by the followingsiexarnpleszi' I Example I V Am -"acid copper batha of the following composition was preparedt cuso s aq.... a.;-fi.. ==a..a..agr/l 200 HaSQt. g. /Lt... ,Thiourea g 10 Pyridine mg./l 40 This bath was brought at a temperature of 30 C. and was kept in motion by blowing in a current of air. The anode was of copper. As the cathode a 50 cm. long iron tube with a diameter of 3.5 cm. and a wall thickness of 2 mm. was connected after it having been subjected as a short pretreatment in a cyanidic copper bath to a socalled copper strike" in which a copper layer of very slight thickness was deposited on the outer wall and on a small part of the inner surface adjacent to the ends. The cathode current density of the main treatment in 1 the acid copper bath according to the invention was adjusted to 8 a./dm. and in 20 minutes 32; of copper was deposited on the tube. The copper layer was soft and lustrous, and the numerous unevennesses originally present on the surface of the tube, had substantially disappeared after the electro-deposition of the copper in the above-described bath.

' Example II An acid copper bath of the following composition was prepared: 7

015045 aq g./l. 250 H2804 ..g./l 2,0 Ammonium sulphate g./l 20 Acetyl thiourea mg./1 20 Caffeine rng./l 50 In this bath an iron plate of 4.5 x 25 dm. was provided with a copper layer at a bath temperature of 25 C. and

Example III An acid copper bath of the following composition was prepared:

Copper fiuoborate ..g./l 400 Fluoboric acid g./l 50 Thiourea mg./l 12 Hexamethylene tetramine mg./l 800 An acid copper bath of the following composition was prepared:

CuSO4.5 aq g./l 250 H2804 g./l 20 Ammonium sulphate g./l 20 Allyl thiourea mg./l 20 Morpholine mg./l 45 A number of small iron plates of 6 x 6 cm. (thickness 0.2 cm.) which had been ground with emery beforehand were provided with a copper layer during 40 minutes at 26 C. in the above-mentioned bath which was kept in motion with air. The cathode current density amounted to 6 a./dm. and the duration of the treatment was 35 minutes. The thickness of the layer was 4211.,

but it is more important that nothing could be seen anymore of the grinding scratches originally present.

What is claimed is:

1. A bright copper plating bath comprising copper sulfate, sulfuric acid, a brightener in proportion of 5 to mg. per liter of solution, said brightener being selected from the group consisting of thiourea, allylthiourea and acetylthiourea, and a filler selected from the group consisting of xanthine and its methyl homologues, hexamethylene tetramine, pyridine and morpholine.

2. A bath according to claim 1, wherein said brightener is thiourea.

3. A bath according to claim 1, wherein said brightener is allylthiourea.

4. A bath according to claim 1, wherein said brightener is acetylthiourea.

5. A bath according to claim 1, wherein said filler is xanthine.

6. A bath according to claim 1, caffeine.

7. A bath according to claim 1, theobromine.

8. A bath according to claim 1, theophylline.

9. A bath according to claim 1, hexamethylene tetramine.

wherein said filler is wherein said filler is wherein said filler is wherein said filler is References Cited in the file of this patent UNITED STATES PATENTS 2,391,289 Beaver Dec. 18, 1945 2,700,020 Pierce Jan. 18, 1955 FOREIGN PATENTS 461,186 Canada Nov. 22, 1949 

1. A BRIGHT COPPER PLATING BATH COMPRISING COPPER SULFATE, SULFURIC ACID, A BRIGHTENER IN PORPORTION OF 5 TO 50 MG. PER LITER OF SOLUTION, SAID BRIGHTENER BEING SELECTED FROM THE GROUP CONSISTING OF THIOUREA, ALLYLTHIOUREA AND ACETYL.THIOUREA, AND A FILLER SELECTED FROM THE GROUP CONSISTING OF XANTHINE AND ITS METHYL HOMOLOGUES, HEXAMETHYLENE TETRAMINE, PYRIDINE AND MORPHOLINE. 